The present invention is related to a calcium phosphate cement, and in particular to a process for preparing a neutral and fast-setting paste from calcium phosphate cement having an improved short time strength, for use in dental and bone prosthesis.
A calcium phosphate cement (abbreviated as CPC) has been widely used as an implant or filling material in dental and bone prosthesis, and its technical details can be found in many patents, for examples U.S. Pat. Nos. 4,959,104; 5,092,888; 5,180,426; 5,262,166; 5,336,264; 5,525,148; 5,053,212; 5,149,368; 5,342,441; 5,503,164; 5,542,973; 5,545,254; 5,695,729 and 5,814,681. In general, the prior art calcium phosphate cements suffer one or more drawbacks as follows: 1) additives having a relatively poor bioactivity being required; 2) a complicated preparation process; 3) an undesired setting time or working time of CPC, which are difficult to be adjusted; 4) not capable of being set to a desired shape in water, blood or body fluid; and 5) poor initial strength after setting of the CPC.
U.S. Pat. No. 5,180,426 discloses a composition for forming a gum-like calcium phosphate type setting material prepared from powder comprising at least one of xcex1-tricalcium phosphate and tetracalcium phosphate; and a setting solution comprising an aqueous acidic solution having dissolved therein a binding agent in such an amount so that the setting solution has a viscosity of 70 centipoises or more.
An object of the present invention is to provide a paste of calcium phosphate cement which is substantial neutral, non-dispersive in water or an aqueous solution and fast setting.
Another object of the present invention is to provide a process for preparing a paste from calcium phosphate cement, which is substantial neutral, non-dispersive in water or an aqueous solution and fast-setting.
Still another object of the present invention is to provide a composition for preparing a paste of calcium phosphate cement, which is substantial neutral, non-dispersive in water or an aqueous solution and fast-setting.
A further object of the present invention is to provide a method of treating a bone or a tooth having a defect in a patient by using a calcium phosphate cement.
In order to accomplish the aforesaid objects of the present invention, a process for preparing a paste from calcium phosphate cement in accordance with the present invention comprises the following steps:
a) mixing an aqueous acidic solution and powder comprising at least one of tricalcium phosphate and tetracalcium phosphate; and
b) mixing the resulting mixture from step a) and an aqueous basic solution to form a paste.
Preferably, the mixing in step a) comprising grinding or stirring a mixture of the powder and the aqueous acidic solution for a period of 1-10 minutes, more preferably about 5 minutes, so as to form a homogenous mixture.
Preferably, the resulting paste from step b) has a pH value of about 6.5-8.5 within a period of 30 minutes from the formation of the paste.
Preferably, the mixing in step b) comprising stirring a mixture of the homogenous mixture from step a) and the aqueous basic solution for a period of less than 10 minutes, more preferably less than one minute, so as to form the paste.
The paste prepared according to the process of the present invention is substantial neutral, non-dispersive in water or an aqueous solution and fast setting, so that the paste has an improved short time strength, e.g. an improved strength measured at about the 45th minute from the starting of the preparation thereof including removing a cast from a mold and immersing the cast in 37xc2x0 C. deionized water at the 15th minute, and measuring the strength immediately following the removal of the immersed cast from water at the 45th minute.